I think what erob3 is missing is that the P.38 is a locked breech pistol, like the Model 1911 or the Luger. With low power cartridges, like the .22 LR or the .32 ACP, the weight (mass) of the slide is enough to hold it in place against the pressure of the cartridge until the bullet exits the barrel and the pressure drops.
But with a high power cartridge like the 9mm Luger or the .45 ACP, the designer has to either make the slide massive (for example the Hi Point) or somehow keep the barrel and slide locked together long enough for the pressure to drop. Else, the slide will move too soon and the internal pressure in the cartridge would burst the case and release high pressure gas, destroying the gun and possibly injuring the shooter.
In the P.38, "keeping the lid on" is done by the locking block holding the slide to the barrel until pressure drops, at which point the locking block is disengaged, allowing the slide to move backward to extract and eject the empty case, then come forward to pick up a fresh round and go back "into battery" with the barrel. To do this, the barrel has to move, as you see.
All of this is accomplished by recoil (not the case pushing against the slide as many folks think), and guns that work like that are called "recoil operated". Not only pistols are operated by recoil; Browning machineguns (except the BAR) are all recoil operated as are the old Remington 8 and 81 semi-auto rifles. Most semi-auto or selective fire rifles today, as well as almost all machineguns, are gas operated; the breech is locked until gas tapped from the barrel after the bullet passes operates the mechanism to open the bolt.
Jim
But with a high power cartridge like the 9mm Luger or the .45 ACP, the designer has to either make the slide massive (for example the Hi Point) or somehow keep the barrel and slide locked together long enough for the pressure to drop. Else, the slide will move too soon and the internal pressure in the cartridge would burst the case and release high pressure gas, destroying the gun and possibly injuring the shooter.
In the P.38, "keeping the lid on" is done by the locking block holding the slide to the barrel until pressure drops, at which point the locking block is disengaged, allowing the slide to move backward to extract and eject the empty case, then come forward to pick up a fresh round and go back "into battery" with the barrel. To do this, the barrel has to move, as you see.
All of this is accomplished by recoil (not the case pushing against the slide as many folks think), and guns that work like that are called "recoil operated". Not only pistols are operated by recoil; Browning machineguns (except the BAR) are all recoil operated as are the old Remington 8 and 81 semi-auto rifles. Most semi-auto or selective fire rifles today, as well as almost all machineguns, are gas operated; the breech is locked until gas tapped from the barrel after the bullet passes operates the mechanism to open the bolt.
Jim